This invention relates to improvements in a power source apparatus for wire electric discharge machining for supplying machining electric power to a gap between a wire electrode and a workpiece used in wire electric discharge machining for generating an electric discharge in the gap between the wire electrode and the workpiece to machine the workpiece.
Electric discharge machining has built a steady position as a machining technique of a mold etc. and has been frequently used in fields of mold machining of automobile industry, home electrical appliance industry, semiconductor industry and so on.
FIG. 8 is an explanatory diagram of a mechanism of electric discharge machining and in the drawing, numeral 1 is an electrode, and numeral 2 is a workpiece, and numeral 3 is an arc column, and numeral 4 is machining liquid, and numeral 5 is a work scrap generated by electric discharge machining. Removal machining of the workpiece 2 by an electric discharge proceeds while repeating the following cycles (a) to (e) (corresponding to FIGS. 8A to 8E). That is, (a) is formation of the arc column 3 by generation of an electric discharge, and (b) is local melt and vaporization of the machining liquid 4 by heat energy of the electric discharge, and (c) is occurrence of vaporization explosive force of the machining liquid 4, and (d) is scattering of a melt part (work scraps 5), and (e) is cooling by the machining liquid, solidification and an insulation recovery of a gap.
This invention relates to wire electric discharge machining used in boring machining, cutting machining, etc. among electric discharge machining. In the wire electric discharge machining, a demand for high accuracy particularly grows and, for example, in machining of a high-accurate mold used in semiconductor industry etc., high machining accuracy of the order of 1 to 2 xcexcm has been demanded.
FIGS. 9A to 9C are explanatory diagrams showing an example of a machining process of wire electric discharge machining and in the drawing, numeral la is a wire electrode, and numeral 2 is a workpiece, and numeral 4a is water which is machining liquid, and numeral 6 is an initial hole, and FIG. 9A shows a first cut which is rough machining, and FIG. 9B shows a second cut which is semi-finishing machining after the rough machining, and FIG. 9C shows a situation of a third cut which is final finishing machining.
A machining example of the first cut of FIG. 9A shows machining for passing the wire electrode 1a through the initial hole 6 and boring the workpiece 2. In the case of such a first cut, since surface roughness and accuracy are finished in the subsequent machining, strict surface roughness and accuracy are not very required and it is important to increase a machining speed particularly in order to improve productivity. In the wire electric discharge machining, in order to increase the machining speed, the water 4a is jetted to a gap to efficiently eject work scraps from the gap. Also, in order to eliminate variations in the jet of the water 4a to the gap to prevent a break in the wire electrode 1a, a method for storing the water 4a in a machining bath (not shown) to immerse the workpiece 2 is used. In this manner, machining liquid supply means for supplying the machining liquid to the gap is used.
In the conventional wire electric discharge machining method as described above, machining of the second cut (FIG. 9B) and the third cut (FIG. 9C), etc. after the first cut (FIG. 9A) is also performed in the water 4a which is machining liquid.
When a voltage is applied to a gap between the wire electrode 1a and the workpiece 2, mutually attractive force acts in a plus polarity and a minus polarity, so that the wire electrode 1a with small rigidity is pulled to the side of the workpiece 2 by this electrostatic force. This causes vibration of the wire electrode 1a and there was a problem that high-accurate machining becomes difficult due to such vibration.
Also, in a state in which vaporization explosive force of the machining liquid occurs by electric discharge energy (for example, FIG. 8C), large force in a direction opposite to the workpiece 2 acts on the wire electrode 1a by the vaporization explosive force of the machining liquid and vibration occurs. Due to such vibration, there was a problem that unevenness occurs in a shape of the workpiece 2 and leads to a deterioration of accuracy.
In semiconductor industry etc. which are use fields of the wire electric discharge machining, for example, in machining of a mold etc. of an IC lead frame, a use in which extremely high accuracy and very smooth surface roughness are required with respect to a workpiece with shape accuracy of 1 xcexcm and surface roughness of 1 xcexcmRmax or less increases and particularly in such a use, the problems caused by the vibration etc. of the wire electrode as described above were remarkable.
FIG. 10 is a block diagram showing a configuration of a conventional power source apparatus for wire electric discharge machining, and in the drawing, numeral 1a is a wire electrode, and numeral 2 is a workpiece, and numeral 7 is a DC power source for supplying a DC voltage to a gap between the wire electrode 1a and the workpiece 2, and numeral 8 is switching means, and numeral 9 is control means for performing on-off control of the switching means 8, and numeral 10 is a gap resistor. A configuration in which the gap resistor 10 is added to the gap between the wire electrode 1a and the workpiece 2 and residual energy due to the presence of a floating capacitance etc. of the gap is consumed is adopted.
FIG. 11 is an explanatory diagram showing a gap voltage waveform in the conventional power source apparatus for wire electric discharge machining of a circuit configuration as shown in FIG. 10 and in the drawing, V is a gap voltage, and T1 is applied time of a voltage pulse, and Tr is pause time. After turning off the switching means 8, the gap voltage V decreases exponentially and a fall of the gap voltage V cannot be performed speedily.
Also, a power source apparatus for electric discharge machining capable of improving machining quality of a workpiece and preventing electrolytic corrosion by changing a polarity of a voltage pulse every voltage pulse of a predetermined number is disclosed in JP-A-1-257513, but there is no disclosure with regard to the fact of speedily performing a fall of the voltage pulse in a gap, and a voltage remaining in the gap after the completion of voltage application does not fall speedily, so that there were problems that time in which it has become higher than or equal to a voltage capable of starting an electric discharge is present and it is difficult to suppress occurrence of an electric discharge during this time and so on.
In the conventional power source apparatus for wire electric discharge machining as described above, there was a problem that it is difficult to shorten pause time since it takes time for consumption of the residual energy of the gap. Also, there was a problem that a possibility of an electric discharge beyond control is left until it becomes lower than or equal to a voltage capable of starting an electric discharge and machining quality reduces.
This invention is performed to solve the problems as described above, and an object of the invention is to obtain a power source apparatus for wire electric discharge machining capable of implementing wire electric discharge machining with high reliability suitable for high-accurate machining.
A power source apparatus for wire electric discharge machining according to this invention as characterized in that in a power source apparatus for wire electric discharge machining capable of applying voltages of both of positive and opposite polarities to a gap between a wire electrode and a workpiece, comprising a DC power source for supplying a DC voltage to the gap between the wire electrode and the workpiece, switching means for performing switching of the DC voltage and control means for performing on-off control of the switching means, and there is provided control means for applying a first voltage pulse to the gap for predetermined time and then applying a second voltage pulse of a polarity opposite to the first voltage pulse for predetermined time necessary for the gap voltage to become a predetermined voltage lower than or equal to a voltage capable of starting an electric discharge corresponding to each machining condition in the inside of machining liquid, the inside of mist or the inside of gas, and use is made in machining for performing at least two machining of machining in the inside of the machining liquid, machining in the inside of the mist and machining in the inside of the gas in combination.
Also, a power source apparatus for wire electric discharge machining according to this invention is characterized in that in a power source apparatus for wire electric discharge machining capable of applying voltages of both of positive and opposite polarities to a gap between a wire electrode and a workpiece, comprising a DC power source for supplying a DC voltage to the gap between the wire electrode and the workpiece, switching means for performing switching of the DC voltage and control means for performing on-off control of the switching means, and there are provided voltage detection means for detecting a voltage of the gap, voltage comparison means for comparing a gap voltage detected by the voltage detection means with a predetermined voltage preset to a voltage or lower capable of starting an electric discharge corresponding to each machining condition in the inside of machining liquid; the inside of mist or the inside of gas, and control means for performing on-off control of the switching means so as to apply a first voltage pulse to the gap for predetermined time and then apply a second voltage pulse of a polarity opposite to the first voltage pulse and complete the application of the second voltage pulse when it is detected that the gap voltage becomes the predetermined voltage by the voltage comparison means, and use is made in machining for performing at least two machining of machining in the inside of the machining liquid, machining in the inside of the mist and machining in the inside of the gas in combination.
Also, a power source apparatus for wire electric discharge machining according to this invention is characterized in that in a power source apparatus for wire electric discharge machining capable of applying voltages of both of positive and opposite polarities to a gap between a wire electrode and a workpiece, comprising a DC power source for supplying a DC voltage to the gap between the wire electrode and the workpiece, switching means for performing switching of the DC voltage and control means for performing on-off control of the switching means, and there are provided voltage detection means for detecting a voltage of the gap, voltage comparison means for comparing a gap voltage detected by the voltage detection means with a predetermined voltage preset to a voltage or lower capable of starting an electric discharge corresponding to each machining condition in the inside of machining liquid, the inside of mist or the inside of gas, and control means for performing on-off control of the switching means for applying a first voltage pulse to the gap for predetermined time and then applying a second voltage pulse of a polarity opposite to the first voltage pulse so that the gap voltage becomes within a predetermined voltage lower than or equal to a voltage capable of starting an electric discharge by a comparison value through the voltage comparison means, and use is made in machining for performing at least two machining of machining in the inside of the machining liquid, machining in the inside of the mist and machining in the inside of the gas in combination.
Also, a power source apparatus for wire electric discharge machining according to this invention is characterized in that after the completion of application of the first voltage pulse, the second voltage pulse is applied after a lapse of predetermined time for prevention of breakage of the switching means.
Also, a power source apparatus for wire electric discharge machining according to this invention is characterized in that in a power source apparatus for wire electric discharge machining capable of applying voltages of both of positive and opposite polarities to a gap between a wire electrode and a workpiece, comprising a DC power source for supplying a DC voltage to the gap between the wire electrode and the workpiece, switching means for performing switching of the DC voltage and control means for performing on-off control of the switching means, and there are provided voltage detection means for detecting a voltage of the gap, voltage comparison means for comparing a gap voltage detected by the voltage detection means with a predetermined voltage preset to a voltage or lower capable of starting an electric discharge corresponding to each machining condition in the inside of machining liquid, the inside of mist or the inside of gas, average voltage detection means for detecting an average voltage of the gap, average voltage comparison means for comparing the average voltage of the gap detected by toe average voltage detection means with zero volt, and control means for performing on-off control of the switching means for applying a first voltage pulse to the gap for predetermined time and then applying a second voltage pulse of a polarity opposite to the first voltage pulse so that the gap voltage becomes within a predetermined voltage lower than or equal to a voltage capable of starting an electric discharge by a comparison value through the voltage comparison means and performing on-off control of the switching means for applying a third voltage pulse of a polarity opposite to the first voltage pulse for predetermined time and then applying a fourth voltage pulse of a polarity equal to the first voltage pulse so that the gap voltage becomes within a predetermined voltage lower than or equal to a voltage capable of starting an electric discharge by a comparison value through the voltage comparison means and performing control so as to make the average voltage of the gap at intervals of predetermined time to zero by a comparison value through the average voltage detection means, and use is made in machining for performing at least two machining of machining in the inside of the machining liquid, machining in the inside of the mist and machining in the inside of the gas in combination.
Also, a power source apparatus for wire electric discharge machining according to this invention is characterized in that a predetermined voltage lower than or equal to a voltage capable of starting an electric discharge at the time of applying the second voltage pulse or a predetermined voltage lower than or equal to a voltage capable of starting an electric discharge at the time of applying the fourth voltage pulse is set near to the voltage capable of starting the electric discharge.
Also, a power source apparatus for wire electric discharge machining according to this invention is characterized in that after the completion of application of the first voltage pulse, the second voltage pulse is applied after a lapse of predetermined time for prevention of breakage of the switching means, and after the completion of application of the third voltage pulse, the fourth voltage pulse is applied after a lapse of predetermined time for prevention of breakage of the switching means.
Since the power source apparatus for wire electric discharge machining according to this invention is constructed as described above, there is shown an effect capable of obtaining a power source apparatus for wire electric discharge machining capable of implementing wire electric discharge machining with high machining quality and high reliability suitable for high-accurate machining. Also, there is shown an effect capable of obtaining a power source apparatus for wire electric discharge machining capable of shortening machining time while preventing electrolytic corrosion of a workpiece.